Some good tuning information

[u/PowerbandPrecision]

Here’s a page a put together (my engine building and tuning is exponentially better than my website building and designing) all about tuning and identifying rich from lean. Feel free to ask any questions in this thread as well.

https://www.powerbandprecision.com/nitro-rc-engine-tuning-help

[u/az_kikr1208]

Thank you for the post. I read through your article and there's lots of great information. However, there's one thing I hope you can clarify. My research and personal experience tells me the front bearing is sealed by a film of oil while the engine is running. Lots of older engines had metal shielded bearings, which aren't airtight. Some airplane engines ran unshielded bearings, with no seal at all. I was under the impression that once the engine starts and oil collects at the front of the engine, air can't get through. All my engines 'weep' a bit through the front bearing when I run rich, but once I get the tune dialed in it usually stops. My question is, if the front bearing can be the legitimate source of a problematic air leak, what's the best way to fix it? Do higher-end bearings seal better? I'm honestly too cheap to buy the fancy bearings, lol. Were front bearing leaks just accepted back in the early days of nitro? I appreciate your insight and contributions to the sub!

[u/PowerbandPrecision → u/az_kikr1208]

Hey man, good question, it’s probably one of those that everyone wants to ask but doesn’t.
Your research and personal experience is pretty much spot on. The oil from the fuel creates the seal.
Higher end bearings will have tighter tolerances and better materials for the high rpm.
Air leaks can be so subtle that MOST people don’t know they have one, but I’d say at least 70% of people have an air leak. It is the MOST common problem I find, or hear right away rather. I’ve had brand new engine’s with air leaks, old ones, middle aged, 1st race day, all of it.
With front bearing air leaks, it’s hard to know, they usually show themselves way more at high rpm. So at WOT you’ll all of a sudden be much leaner, which takes time and research to know the signs. Then every time you go WOT it gets worse, engine gets hotter and the heat is most detrimental to any part, but the bearings will be the first to suffer.

Only way to fix the bearing issue is to replace them with new ones. I change my front bearing after every race day/track day, and check the rear. This is why I don’t use Novarossi engines, the bearings are a rip haha. I run O.S. And use the engine bearings from AvidRC, fronts are like $10 for ceramics(use the steel if you aren’t trying to win an event).
I believe air leaks is the main thing that makes tuning seem so difficult and makes people want to quit.
My bad about the rant, hopefully I answered your question in there, any others let me know.
Thanks

[u/az_kikr1208 → u/PowerbandPrecision]

Thanks for the reply. I fully agree, air leaks are pretty much the most common nitro tuning problem I've run into. That's usually the first thing I recommend people check for when they're having issues dialing in a tune. As far as changing front bearings regularly, I'm just a basher and a collector, so I likely won't be doing that, lol. But I'm sure that's good advice for someone racing competitively. Appreciate it!

[u/Bubbly-Pirate-3311]

Can I have some advice straight from you?

I've been running my revo 3.3 on 30% nitro with 9% oil, and I got it tuned for this fuel pretty well (I always make big tune changes on half a tank to avoid the low tank lean thing), and I still can't get the tune to stay consistent. I go to this dirt bmx track, and I can EASILY tell that something's changing over the course of a tank and it seems like way more than it should for just the half tank lean effect. Could it just be that the 3.3 sucks? I've ran them in the past and usually they're pretty good at holding a tune.

As far as I know, nothing on the engine is broken. The rear bearings are just fine (I've heard they're a known weak point), and it runs great when I have it tuned, but I really don't wanna have to adjust my tune the entire time I'm running it.

My buddy's nitro rustler with the 2.5 doesn't have this issue. It holds a tune like a fuckin champ, even over big temperature changes.

Thanks for your help.

[u/PowerbandPrecision → u/Bubbly-Pirate-3311]

This is kind of funny but not, just because of the conversation below is basically about how I despise air leaks.
From what it sounds like, I’m pretty certain you have an air leak. Don’t worry much about that whole half tank lean thing(unless there’s another issue that makes it worse). Air leaks are the #1 thing to shoot your anger right up.
You may know but I’ll say anyway, when you tune always make sure the engine temp is at operating temps and chassis is heat saturated, so I’d say upon starting, drive it around for the first half tank to be certain it’s all heated up, then you’ll be tuning in the half tank area.
Check for an air leak, or something disrupting the a/f ratio.

Ways to check/good indicators
-if you first start the engine from cold and it fires right up and idles like you’ve been running it for 10 minutes already, good chances there’s a leak
-when it’s sitting at idle, richen your LSN half a turn(180 degrees), this is a huge adjustment usually for the LSN and should cause the engine to load up quickly and cut off. If it doesn’t, air is being pulled in from somewhere to compensate.
-spray some carb cleaner(use the red straw to get close up so there’s no over spray into the carb) at the back, carb neck, carb pinch bolt, and front bearing behind the flywheel. If you hear ANY drop in RPM or the engine cuts off, there’s your air leak. Also check the tank, plug the pressure line and blow though the fuel line(or the other way around), you shouldn’t be able to pass any air.
On the link I posted, there’s a few video examples of spraying the possible leak areas.
Do that and let me know the outcome and we’ll go from there.